The invention relates to a process for the induction hardening of crankshafts with at least one connecting-rod pin and with at least two main bearings, in particular for the hardening of the at least one connecting-rod pin, by means of a contactlessly operating inductor, the crankshaft performing a rotational movement during the hardening of the at least one connecting-rod pin. Furthermore, the invention relates to an apparatus for carrying out the process.
A process of the generic type is known from U.S. Pat. No. 6,013,904. In this case, the crankshaft is clamped at both its ends and rotated at a certain, but in itself variable speed. In order in this process to harden not only the main bearings but also the connecting-rod pins, the inductor is arranged on a handling device which continuously follows the rotational movement of the connecting-rod pin. As a result, contactless hardening of the crankshaft is possible, which is intended to lead to a shorter working time overall in the hardening of the crankshaft.
However, such constant tracking by the inductor is very complicated and is susceptible to wear and faults. The possible occurrence of runouts, in other words inaccuracies of the workpiece, can still cause undesired contact of the workpiece with the tool. Furthermore, a very complicated control system is required for the constant tracking by the inductor. Finally, the process described above And the associated apparatus make very high demands on the operating personnel, which inevitably leads to higher wage costs and consequently workpiece costs.
A similar state of the art is also shown by DE 40 29 724 C2, it being intended here, in contrast with U.S. Pat. No. 6,013,904, that the coupling distance between the tool and the workpiece be set such that it is smaller at subregions of the surface of the workpiece which have a high heat dissipation than at subregions of the surface of the workpiece which have a low heat dissipation. This is intended to achieve a homogeneous hardness profile within a fast cycle, i.e. in a short time.
However, this apparatus and the associated process have similar disadvantages to those already stated above.
It is therefore the object of the present invention to provide a process and an apparatus for the induction hardening of the connecting-rod pins of crankshafts by means of which contactless hardening is possible with comparatively little effort. At the same time, as little tool wear as possible and simple operator control are to be provided.
This object is achieved according to the invention by the center axis of the at least one connecting-rod pin to be hardened being used as the axis for the rotational movement of the crankshaft.
By using the center axis of the at least one connecting-rod pin to be hardened as the axis for the rotational movement of the crankshaft, i.e. by shifting the center axis of the connecting-rod pin toward the rotational axis of the crankshaft, the region of the crankshaft that is respectively to be hardened, in the present case the connecting-rod pin, no longer performs an eccentric movement about a point but a purely rotational movement about its center axis or, in other words, a movement that is coaxial-concentric to the rotational center axis. For this reason, the inductor no longer has to track the connecting-rod pin to be hardened, but can remain in one and the same place during the entire hardening operation for the individual connecting-rod pin. This makes the process very much easier to control, since constant tracking movements are not necessary, and there is advantageously the combined effect that easier control is possible and the movement of the mechanical parts is reduced to a minimum.
Furthermore, this results in a relatively simple and consequently easy-to-operate and fault-insusceptible process, which leads to low wear of the inductor and consequently also to low downtimes when carrying out the process. According to the invention, contactless hardening of the crankshaft is now possible, which in addition to lower wear of the inductor leads to shorter heating times and consequently makes it possible to achieve a gain in cycle time and is also accompanied by smaller heat inflow zones. The rotation during hardening advantageously leads to a very homogeneous hardening zone. The relatively great extent to which the inductor wraps around the connecting-rod pin in this case creates a clearance in the coupling dimension, in other words the distance between the crankshaft and the inductor. This allows compensation for a possibly occurring circularity runout of the crankshaft within certain limits.
The process according to the invention may be advantageously carried out in a wide variety of ways and with a wide variety of degrees of automation, which leads to very great flexibility in the hardening of crankshafts.
When hardening crankshafts with a plurality of connecting-rod pins arranged offset in relation to one another, it may be provided in a particularly advantageous embodiment of the invention that, for hardening the second connecting-rod pin, arranged offset in relation to the first connecting-rod pin, the crankshaft is pivoted by an angle corresponding to the angle between the first connecting-rod pin and the second connecting-rod pin. Since the angles referred to between the connecting-rod pins are always known, very high precision is possible here, leading to a good hardening result. It goes without saying that this procedure may also be transferred from the second connecting-rod pin to the third connecting-rod pin and generally in each case to the next-following connecting-rod pin.
If the crankshaft to be hardened has a plurality of connecting-rod pins in line with one another, it may be advantageous on the one hand to harden them by means of one inductor, the inductor then having to be transported over a corresponding distance in the axial direction after the hardening of one connecting-rod pin. As an alternative to this, it is also possible to harden a plurality of connecting-rod pins in line with one another simultaneously by means of a corresponding number of inductors. Depending on the configuration of the crankshaft to be hardened and on the possibility dependent on this of providing inductors, one of the two possibilities mentioned will be more advantageous.
To achieve a heat distribution that is as uniform as possible within the overall heated region of the crankshaft, it may be provided in a further advantageous embodiment of the invention that the power of the inductor is changed in a way corresponding to the geometrical shape of the crankshaft web adjoining the connecting-rod pin to be hardened.
An apparatus for carrying out the process is provided by the features of claim 8.
The at least one inductor, the rotating device and the adjusting device according to the invention provide an apparatus which, compared with already known hardening apparatuses for crankshafts, is of a simple and consequently easy-to-operate construction and in which only little maintenance effort is required on account of, inter alia, the contactless hardening operation.
A very great amount of heat is introduced into the region of the crankshaft to be hardened if, in an advantageous embodiment of the apparatus according to the invention, the inductor encloses the connecting-rod pin to be hardened at least over half its circumference.
A configuration of the inductor that is very simple and inexpensive to produce can be provided by the at least one inductor being produced by machine production.
In a further advantageous refinement of the invention, a pivoting device which is capable of pivoting the crankshaft by a certain angle about its center axis may be provided.
An a result, in the case of crankshafts with connecting-rod pins arranged offset in relation to one another, it is possible in a very simple way to pivot the connecting-rod pin respectively to be hardened into the rotational axis of the hardening apparatus.